A group of students participated in an experiment to study the association between resting heart rate and exercise heart rate under various exercise conditions. Study participants stepped at a frequency of 14 steps per minutes (Level 0), 21 steps per minute (level 1), and 28 steps per minute (level 2). To investigate the relationship between resting and exercise heart rate and to see the effects of step frequency on the relationship, a scatterplot might be created by:
plotting resting heart rate on the y-axis and exercise heart rate on the x-axis.

a. plotting exercise heart rate on the y-axis and step frequency on the x-axis.
b. using separate symbols for the different step frequencies to see if the relationship is affected by step frequency while plotting resting heart rate on the x-axis and exercise heart rate on the y- axis.
c. There is to much information in this study to be able to fit it all on one graph.